(-Lactam antibiotics, specifically third-generation cephalosporins, are critical for the treatment of complicated diarrheal illness due to many Category B bacterial food and waterborne pathogens. Their excellent activity against Salmonella (typhi and non-typhi) and Shigella coupled with the fact that they are safe for women and children makes them the sole therapy for complicated pediatric infections with these pathogens and a critical countermeasure for a bioterror attack that employs one of these agents. However, the utility of this class of antibiotics in Enterobacteriaceae is compromised by the rapid spread of new (-lactamase resistance mechanisms, enzymes produced by bacteria that hydrolytically inactivate (-lactam antibiotics. In this application we propose to develop a new, first-in-class, highly potent and broad spectrum (-lactamase inhibitor, PZ-7475. This inhibitor rescues the activity of (-lactam antibiotics against strains of Enterobacteriaceae (including Salmonella and Shigella spp.) that express Ambler class A, C and D (- lactamase enzymes. In addition to its excellent safety and physiochemical properties, PZ-7475 has a long plasma half life, uniquely positioning it to be used in combination with ceftriaxone, the once-a-day, workhorse parenteral (-lactam for important Category B bacterial food and water-borne pathogens. During the course of the requested 3-year Grant funding we intend to: (a) advance PZ-7475 in combination with ceftriaxone through the first stages of Preclinical development, particularly concentrating on aspects critical to Category B; (b) identify and advance back-up compounds to PZ-7475 as a contingency; and (c) develop an orally bioavailable beta-lactamase inhibitor through synthesis and testing of analogues of PZ-7475 and ester prodrugs thereof. An oral (-lactamase inhibitor will ultimately be combined with orally bioavailable cefpodoxime proxetil for mass administration in the event of a bioterror attack with a category B Enterobacteriaceae expressing natural or engineered (-lactamase resistance mechanisms. Relevance: The developed combination of the (-lactamase inhibitor PZ-7475 with ceftriaxone will preserve the efficacy of this vital (-lactam antibiotic as a countermeasure to a bioterror attack with (-lactam-resistant Category B Enterobacteriaceae pathogens as well as for treatment of both complicated pediatric diarrheal illness and serious gram negative infections in the hospital setting. The development of an orally available (-lactamase inhibitor-cefpodoxime combination will offer an important therapeutic option for mass administration in the event of a bioterror attack with a category B agent.